1. Field of the Invention
The present invention relates to an organic light emitting device (OLED) and a method of fabricating the same and more particularly, to an OLED having an organic active layer with a new molecular orientation structure and a method of fabricating the OLED in which the organic active layer is formed using a solution process.
2. Description of the Related Art
Organic light emitting devices (OLED), which include an anode, a cathode, and an organic active layer including a fluorescent or phosphorescent organic compound between the anode and the cathode, are self-emissive devices which spontaneously emit light as holes supplied from the anode and electrons supplied from the cathode combine with each other. Generally, the organic active layer includes an organic emission layer (EML), a hole transporting layer (HTL) and a hole injecting layer (HIL) between the EML and the anode, and an electron transporting layer (ETL) between the EML and the cathode.
In general, an OLED fabricated by thermal vapor deposition has a heterojunction structure including an HIL, an HTL, an organic EML, and a hole barrier layer (HBL), which are formed of heterogeneous materials, in order to obtain an efficient emission structure. In addition, in order to realize a large size OLED display, thickness uniformity of the layers should be ensured. However, it is difficult to form a large-sized organic active layer having a uniform thickness by the conventional vapor deposition process. Thus, recently a method of coating an organic material by a solution process, which is a wet process, has been suggested. In the solution process, a solution of an organic material, having a high solubility, dissolved in a solvent is coated by spin coating, inkjet coating, or the like. However, fundamentally this solution process is not suitable for forming a multi-layer structure because a solvent used to form an upper layer may melt a lower layer.
Meanwhile, Franky So (U.S. Pat. No. 5,925,980), J. J. Brown (Proceedings of SPIE Vol. 4800 (2003)), C. Wu (Appl. Phys. Lett. Vol. 86103506 (2005)), Yang Yang (Appl. Phys. Lett. Vol. 832453 (2003)), and others reported results on efficienty improvement or lifespan increase when a graded junction forming method is used, in which one of the layers in an OLED has the same composition as an adjacent layer, but with a composition gradient.